1. Field of the Invention
The present invention relates to an apparatus and a method for multichannel sequence transmission and control, and more particularly to a control of data transmission and printing for a thermal transfer print head or a thermal print head (TPH).
2. Description of the Prior Art
Due to population of the digital image products and improvements of the printing technique related products and inks, users are easy to print out a photograph with the ordinary printer and the print quality is not worse than the traditional developed photograph. The color printers available in the market are classified into the color inkjet printer, the color laser printer, and thermal transfer printer. The printout of the inkjet printer is easy to be more or less spread with the ink to blur the image printed on the paper. Furthermore, the printing speed of the inkjet printer is slow. The printing quality and speed of the laser printer are better than the inkjet printer, but the price of laser printer is too high for general users. The printing speed of thermal transfer printer is faster, and the printout of the thermal transfer printer has a good printed quality and a water-resistant coating. Moreover, the cost of the thermal transfer printer is cheaper. Therefore, the thermal transfer printer has become the mainstream in the printer market gradually.
The data-transmission and printing method of the conventional thermal transfer printer will be described in the following. First, the contents desired to print, comprising words, and pictures, are transmitted in column/row-based transmission method controlled by an external microcontroller, such as CPU or MCU, to a shift register in a print head sequentially. Next, the column/row-based contents in the shift register are transmitted to and stored in the latch register via a latch signal set by a control unit. Plural heating units, which correspond to the latch register, are enabled by strobe signals generated by a strobe signal generator to heat the respective color ribbon for the surface of a printed media, such as a paper or photographic paper, being printed with a predetermined column/row content through the heated ribbon. And then, the printed paper is moved by a rotating axle to the next line to complete the printing of the current predetermined column/row content. The printing process is performed repeatedly till the entire picture being printed onto the surface of the printed media. However, as the data-transmission and printing method described above, the data-transmission and is directly controlled by the external microcontroller. Therefore, the data transmission, the printing speed and the printing quality are directly related to the load of the data process of the microcontroller.
In addition, the print head, which is one of key components of the thermal transfer printer mentioned above, employs plural heating units therein to heat the color ribbon for sublimating dyes in the color ribbon and generating an image on a surface of the printed media. The respective heating unit, which is a thermo-sensitive resistor, heats up gradually when the current flows therein and cools down gradually when the current stops flowing. Therefore, the preceding feature of the respective heating unit is capable of heating the color ribbon to perform the printing operation.
The ribbon applied in the thermal transfer printer is a stable solid state at the room temperature and is sublimated to vaporize when the temperature is higher than a preset critical temperature, wherein the ribbon comprises a plurality of color regions arranged sequentially and each of the color regions has a color dye different from each other. The amount of the dye transferred onto the printed media is based on a vaporized duration of the dye, and the more the dye is, the deeper the gray level is. Hence, to achieve a preferable printing quality, the ribbon has to be heated up to a temperature above the critical temperature for a period of time. Unfortunately, the working temperature of the heating unit has an upper limit, and it can be seen in FIG. 1 that the temperature of the heating unit rises rapidly at the initial heating stage and the heating unit may be damaged when the temperature is over the upper limit.